1. Field of the Invention
The invention relates to a vehicle undercarriage or chassis for a vehicle especially for a four-wheeled, driven vehicle for transporting at least one person.
2. Discussion of Background Information
Vehicle carriages for multi-track motor vehicles, whereby the wheel suspension is provided by torsion springs, are well known and widespread. Thereby, a distinction must basically be made between two different embodiments, namely the crank axle and the cam-lever shaft.
In the crank axle, the wheel axle is arranged on an elastically rotatable arm, whereby the arm changes its angle in relation to the axle suspension with changing wheel load. The return torque usually increases with the change in angle, thus providing a rebound force on the wheel axle that acts in the opposite direction of the forces of inertia. The only degree of freedom for movement in such an arrangement is the elastically limited rotation around the torsion spring element, so that with sufficiently stiff design of the arrangement a defined wheel guidance is obtained in the other directions of movement. The torsion spring element can be designed as a metal rod in the axis direction of the free rotational motion, or as an elastomer spring element that is deformed primarily by shearing. Since each wheel is guided by a separate crank guide, independent capability of movement of the wheels is achieved, i.e. independent wheel suspension. The crank axis represented here is used preferably in load-bearing vehicles with relatively stiff suspension. The torsion spring may have high torsion stiffness, so that it has sufficient stiffness as a guiding element for the additional degrees of freedom of wheel movement. The disadvantage of this embodiment is the fact that in passenger vehicles the suspension must be softer for reasons of comfort. However, with a softer suspension the torsion spring can no longer manage the wheel guidance satisfactorily. Such inadmissible bump steers and camber changes under changing wheel loads lead to an unstable behavior of the vehicle.
In the embodiment with a cam-lever shaft, the spring energy is also stored in a component that counters its twist with the relevant torque. It differs from the crank axle in that further directions of movement can partly be restricted by separate elements. For example, embodiments are known in which only longitudinal guidance of the wheel in the direction of movement is achieved by the spring. Lateral guidance and maintenance of the track and camber angle are provided by the split axle of the wheel drive. With this arrangement, stiff wheel guidance in all directions except the compression is easier to achieve in terms of construction. However, it is also possible to guide solely the compression vertically to the tire contact area using the oscillating lever, whilst defining all the other directions of movement with a suitable wheel suspension. The disadvantage of this design is the high construction cost, which also results in a high degree of failure.
The present invention provides a vehicle undercarriage of the type mentioned at the beginning, which on the one hand avoids the disadvantages described above and on the other hand makes use of the constructional simplicity of the crank axle, whereby the restriction of lacking wheel guidance in the case of soft suspension is avoided.
The invention provides a vehicle undercarriage that includes at least one main frame. The main frame is configured as an arrangement of closed hollow profiles and diametrically opposed torsion springs having axes of revolution crosswise to a direction of travel. The torsion springs are connected to the lateral hollow profiles of the main frame with gusset plates, and a flexurally resistant connecting pin is provided on the torsion springs with an oscillating lever. The connecting pin has a mounting at its ends for the wheels.
The surprising advantage resulting from the above-noted features of the invention lies in the fact that optimal wheel guidance that guarantees stable driving behavior of the vehicle is achieved with an extremely simple construction. By designing the main frame with hollow profiles joined together in such a way as to be flexure- and torsion-resistant, the superstructure of the vehicle itself is also advantageously torsion-resistant. Moreover, the arrangement of the torsion springs offers the advantage that in addition to a high degree of material utilization for the elastic element of the suspension it is also possible to design wheel guidance functions using this suspension. The flexurally stiff connecting pin is provided as wheel guidance element. In addition, this flexurally resistant connecting pin offers the advantage that bump steer and camber change of the wheels are linked more or less rigidly by a connecting pin. Therefore, track width, toe angle and camber angle are invariant towards the plane through the contact points of the wheels on the contact surface.
It is advantageous that an embodiment of the instant invention also includes that all connections between the individual parts are made exclusively with welding joints, since it allows rational manufacturing, possibly even with the use of welding robots.
In an advantageous embodiment the torsion spring includes of two concentrically arranged hollow profiles, whereby at least one elastomer element is provided between the hollow profiles, preferably in the area of mounting of the oscillating lever. In a further advantageous embodiment, the torsion spring includes an outer torsion spring tube, an elastomer spring element and a torsion spring axis. These torsion springs provide a sufficient longitudinal stiffness in the direction of their axis of rotation and on the plane vertical to this axis.
In the embodiment in which the main frame includes of two lateral hollow profiles and two torsion spring tubes configured as a roughly ring-shaped, flexure- and torsion-resistant arrangement, it is possible to achieve optimal flexural and torsion stiffness for the main frame.
In a further embodiment, the connection between the lateral hollow profiles and the torsion spring tubes or other connecting profiles is achieved by preferably flat gusset plates arranged on both sides of the lateral hollow profile. Thus, a torsion-resistant connection of the hollow profiles is achieved by the special arrangement of the gusset plates on both sides of the profile. The gusset plates are necessary in order to connect at least two profiles with any connecting angle with each other rigidly by means of welding. The profiles may have the same vertical parting sections. Unlike gusset plates in conventional framework constructions, in the profile rods of which traction and pressure forces usually occur, flexural and torsion forces also have to be transmitted in this construction.
The gusset plates should be arranged on both sides of the profiles so that the welding seam is located in the neutral plane of the main flexural stress of each connecting profile. As a result, expansion stress on the welding seam in such a case of stress can be avoided. This fact has an advantageous effect on the stability of the welding seam.
Due to the bilateral arrangement of the gusset plates on the connecting profiles, however, stress with a general direction, such as e.g. flexion, torsion, traction or pressure, can be transferred without an unfavorable strain on the welding seams. The type and level of the collective stress has a structural impact on the design of the gusset plate. The construction principle itself remains unaffected.
The advantage of this type of gusset connection includes the fact that separate profile sections, which are easy to manufacture, can be used even for complex framework geometries under any stresses vertical to the profile axis.
The embodiment in which the connecting pin is configured as an open profile with low torsion resistance in the area between the oscillating levers is also advantageous, since profiles of this type unite a high flexural resistance with low torsion resistance.
With the embodiment including a connecting pin having a flexure- and torsion-resistant reinforcement in the area between the oscillating lever (6) and the mounting (8), in particular the steering stub mounting and further embodiment including the connecting pin designed as a hollow profile in the area between the oscillating lever and the mounting, in particular the steering stub mounting, the torsion resistance of the connecting pin can be varied in accordance with the length of reinforcement, and it can be calculated in advance. Since the ratio between flexural stiffness and torsion resistance of a profile rod is variable in many areas with the design of the profile cross-section, the wall thickness, dimensions and/or profile design, it is possible to link the individual compressions of an axle with each other. By increasing the torsion resistance of the connecting pin accordingly, there is stronger coupling of the compression, so that the rolling angle of the vehicle, i.e. rotational movement around the longitudinal axis, can be prevented specifically. This is imperative especially in superstructures that create an elevated vehicle center of gravity.
Embodiments including the oscillating lever being connected rigidly to the connecting pin; or including the oscillating lever being designed so as to have low torsion resistance along its longitudinal axis; or including the oscillating lever having a thin-walled, flat shape are also advantageous. A variable compression invariably causes torsional flexing of the connecting pin in relation to the vehicle superstructure. In this case, twisting is forced upon the oscillating levers, which are connected rigidly to the connecting pin on the one hand, and can exclusively perform a rotational movement crosswise to the direction of travel. Therefore, the oscillating levers should advantageously be designed so as to have low torsion resistance along the longitudinal axis, in order to be able to achieve the necessary axle compression. This may be achieved with a thin-walled, flat design of the oscillating levers. Lateral forces such as those acting on the vehicle with every change in direction would cause an inadmissible deformation of the oscillating levers crosswise to the direction of travel.
Thereby, an embodiment in which the rotation point of the oscillating lever lies on the front connecting pin facing in the direction of travel, on the line of efficacy between the overall center of gravity of the vehicle and the contact point of the wheels proves advantageous, since with the arrangement along this line the point of rotation of the oscillating lever is not additionally stressed by torque due to braking forces during a braking maneuver using the front brakes, as a result of which there is no spring feedback through the braking forces. Of course this arrangement is suitable both for front and rear axles.
An embodiment in which all the hollow profiles have vertical parting sections is also advantageous, since it guarantees rational manufacturing of components, whereby further processing is not required.
The embodiment in which a steering linkage is provided, including a steering rod lever connected rigidly to a steering rod, as well as a relay lever capable of swivelling on the steering rod lever around a rotational axis parallel to the steering rod and which is connected to an eccentric shaft by a crank joint is particularly advantageous, whereby steering of the vehicle is independent of compression as a result of the construction. Normally, the steering rod is connected to the steering arms of the steering stubs via a ball joint. This allows some degree of swivel movement of the steering rod around it longitudinal axis. A relay lever arranged so as to be capable of swivelling around an axis parallel to the steering rod can balance out spacing changes together with the steering lever. A steering lever is mounted rigidly on the steering rod with a hinge at the upper end, the rotational axis of which is parallel to the steering rod. A relay lever is pivoted to the rotational axis of the steering lever, thus being capable of swivelling around an axis parallel to the steering rod. The relay lever is connected to the eccentric shaft so as to be articulated. This construction transfers movements of the eccentric shaft parallel to the steering rod directly to the joints of the steering stubs, but it can balance out the changeable spacing of the eccentric shaft vertical to the steering rod.